When you config(8) a kernel, it is assigned a version number, which will start with zero if this is the first time, or if you have delete the /usr/src/sys/arch/<ARCH>/compile/<KERNEL> directory structure. After that, the version number will increment each time.

There are several ways to see your kernel. For more complete information than uname(1), use either

forgot to say thank you,just notice that,so how would i kept track with the latest kernel for let say as i run 4.5?isn't it hard since there is no exact version?how many times permonth you always update and build the kernel?i mean applying patch and etc,these small patch changes not not consider on big kernel changes?

If you are running -stable, keep track of published errata & rebuild as necessary. Building the kernel, userland, & Xenocara is all covered in Section 5 of the FAQ.

As for 4.5-current, rebuild when features or changes warrant it. Again study Section 5. Also, be very aware of the information found in the Following -current document.

All of your questions of late are valid, but they are covered in detail in the FAQ. Seriously study this document. It is maintained by developers of the Project for a reason -- to be correct, current, & answer questions which most users will ask at one time or another.

As an addendum (& repeating information I've already covered in a different thread...), 4.5-current no longer exists given that the OPENBSD_4_6_BASE CVS tag was created nearly a month ago. The head of CVS is now 4.6-current.